Monitoring Compliance Using Venous Refill Detection

ABSTRACT

Monitoring patient compliance with a compression therapy regimen. Venous Refill Time (VRT) is monitored via a pressure sensor in a bladder of a compression system. A controller of the compression system correlates the monitored VRT to a predetermined threshold to determine whether the patient is using the compression system.

BACKGROUND

Aspects of the present invention generally relate to compressiongarments, and particularly to monitoring use of compression garments.

A major concern for immobile patients and like persons are medicalconditions that form clots in the blood, such as, deep vein thrombosis(DVT) and peripheral edema. Such patients and persons include thoseundergoing surgery, anesthesia, extended periods of bed rest, etc. Theseblood clotting conditions generally occur in the deep veins of the lowerextremities and/or pelvis. These veins, such as the iliac, femoral,popliteal and tibial return, deoxygenated blood to the heart. Forexample, when blood circulation in these veins is retarded due toillness, injury or inactivity, there is a tendency for blood toaccumulate or pool. A static pool of blood may lead to the formation ofa blood clot. A major risk associated with this condition isinterference with cardiovascular circulation. Most seriously, a fragmentof the blood clot can break loose and migrate. A pulmonary emboli canform from the fragment potentially blocking a main pulmonary artery,which may be life threatening. The current invention can also be appliedto the treatment of other conditions, such as lymphedema.

Conventional vascular compression systems include a compression sleeveor garment fluidly connected to a controller for cyclically inflatingthe sleeve. The sleeve wraps around a patient's limb and has one or morechambers, or bladders, inflated to provide compressive pulses to thelimb, typically starting around the most distal portion of the limb(e.g., the ankle) and progressing sequentially toward the heart. Thecyclical inflation of the compression garment enhances blood circulationand decreases the likelihood of DVT. Also, vascular compression systemsmay be applied to the treatment of other conditions, such as lymphedema.

An important monitoring parameter for compression systems is the venousrefilling time (VRT) calculated by the controller, which is the normaltime taken for the veins in the limb to distend with blood aftercompression. Current devices, such as those disclosed in U.S. Pat. No.6,231,532, detect pressure change (e.g., via a pressure sensor) in thesleeve as a function of the change in girth of the limb to measure VRT.In turn, the controller adjusts the cycle of compressive pulsesaccordingly based on the calculated VRT.

Patient compliance with a prescribed compression regimen and usage of acompression system is a common problem. Unfortunately, it is nearlyimpossible in a health service setting for a medical professional toconstantly monitor a patient during use of the system. Therefore a needexists for improved compliance monitoring.

SUMMARY

In general, aspects of the invention relate monitoring a patient'scompliance with a compression therapy regimen based on a determined VRT.In one aspect, a signal is received from a pressure sensor coupled to acompression garment that is sized and shaped to be wrapped aroundsubstantially a limb of a wearer. The signal is indicative of a changeof girth of the limb. A venous refill time of the limb is determined asa function of the received signal and monitored. When the monitoredvenous refill time exceeds a predetermined threshold, a patientcompliance timer is incremented.

A system embodying aspects of the invention monitors patient compliancewith a compression therapy regimen. The system includes a compressiongarment, a compression control unit, and a pressure sensor. The garmentis sized and shaped to be wrapped around substantially a body part of awearer and has one or more fasteners for use in securing the garment ina self-retaining wrapped configuration around the body part. And thegarment comprises one or more selectively inflatable bladders forapplying compression to the body part upon inflation. The compressioncontrol unit comprises a pump for pressurizing fluid and an outlet portin fluid communication with the pump. The outlet port has fluid tubingconnected thereto for selectively delivering pressurized fluid to atleast one of the inflatable bladders. The pressure sensor is coupled toat least one of the bladders and generates a signal indicative of achange of girth of the body part when the garment is in the wrappedconfiguration. The control unit also includes one or more processorsreceiving and responsive to the signal generated by the pressure sensorfor determining a venous refill time of the body part. The processormonitors the determined venous refill time and increments a patientcompliance timer in response to the monitored venous refill timeexceeding a predetermined threshold.

In another aspect, a method of monitoring patient compliance with acompression therapy regimen includes receiving a signal from a pressuresensor coupled to a compression garment. The signal is indicative of achange of girth of a limb when a compression garment is wrappedsubstantially around the limb. The method includes determining a venousrefill time of the limb as a function of the received signal andmonitoring the determined venous refill time. The monitored venousrefill time is compared to a predetermined range of normal venous refilltimes. The method also includes correlating the monitored venous refilltime to determine patient compliance as a function of the comparing.

Other objects and features will be in part apparent and in part pointedout hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a system for monitoring patient compliance witha compression therapy regimen;

FIG. 2A is a front view of a compression garment in an unwrappedconfiguration;

FIG. 2B illustrates the compression garment of FIG. 2A in a wrappedconfiguration adapted for use on a patient;

FIGS. 3A-3E are graphs illustrating exemplary pressure profiles during aprocedure to determine venous refill time according to the presentinvention;

FIG. 4 is a graph illustrating an exemplary customized venous refilldetermination based on the pressure profiles in FIGS. 3A-3E;

FIG. 5A is an interface of the control unit according to an embodimentof the invention;

FIG. 5B is an exemplary display of patient compliance according to anembodiment of the invention;

FIG. 6 is an exemplary flowchart for monitoring compliance according toan embodiment of the invention;

FIG. 7 is an exemplary flowchart for monitoring compliance according toanother embodiment of the invention;

FIG. 8A is a graph illustrating an exemplary pressure cycle of aninflatable bladder when not in use;

FIG. 8B is a graph illustrating an exemplary pressure cycle of aninflatable bladder when in use;

FIG. 9A is a graph illustrating an exemplary pressure profile duringvenous refill determination of an inflatable bladder when not in use;and

FIG. 9B is a graph illustrating an exemplary pressure profile duringvenous refill determination of an inflatable bladder when in use.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION

Referring to FIG. 1, a compression therapy system for monitoring patientcompliance is designated generally by the reference character 10. In anembodiment, system 10 is an intermittent pneumatic compression (IPC)device or the like. The system 10 comprises a garment 14 that can befitted to a limb or other body part of a patient. The garment 14 haswith one or more bladders 18 a-n for applying compression to the limbduring inflation of the bladders. The system 10 also includes a pressuresensor 22 coupled to at least one of the bladders (e.g., bladder 18 b)via, for example, connection tubing, and a compression control unit 26.The control unit 26 monitors patient compliance with a prescribedcompression therapy regimen. Specifically, and as will be described indetail later, control unit 26 determines, or calculates, a venous refilltime (VRT) of the limb based on pressure measurements obtained from thepressure sensor 22. The control unit 26 monitors the determined VRT andincrements an active therapy time or timer if the monitored VRT exceedsa predetermined threshold.

The garment 14, an exemplary embodiment of which is shown in FIGS. 2A-Bwithout any interconnections to the rest of system 10, wrapssubstantially around a limb or body part of the patient. The garment 14has one or more positioning or fitting devices, such as fasteners 30A-F,32A-F, for securing the garment in a self-retaining, wrappedconfiguration around the limb. Desirably, the garment 14 is sized andshaped to fit the limb in a manner that avoids wasted energy typicallyassociated with inflating a loosely fitted garment. Any suitableapproach of determining fit of the garment 14 and accordingly adjustingthe fasteners 30A-F, 32A-F is within the scope of the invention. Suchapproaches may include, but are not limited to, simple user measurementssuch as inserting a finger between the garment 14 and the limb to checkfor fit, and more complex, sensor-based fitting mechanisms formed on thegarment itself

FIG. 2A illustrates the fasteners as hook (30A-F) and loop (32A-F) tabsfor this purpose. FIG. 2B shows the garment 14 in a wrappedconfiguration on a leg of a patient, and illustrates the fasteners30A-F, 32A-F during use. Alternatively, buckles and/or hook and loopwraps may be employed. Any design of the fasteners 30A-F, 32A-F iswithin the scope of the invention. In the exemplary embodimentillustrated in FIGS. 2A and 2B, garment 14 comprises four inflatablebladders 36-39 (referred to as bladders 18 a-n in FIG. 1) forselectively applying compression to the limb upon inflation. Any number,shape, and configuration of the inflatable bladders 36-39 is within thescope of the invention.

Referring again to FIG. 1, the compression control unit 26 is operablefor controlling operation of the compression system 10. A pump 42 of theunit 26 connects to a fluid supply 46 and provides a fluid (e.g.,compressed air) to the bladders 18 a-n via connection tubing.Specifically, an outlet port 50 of the pump 46 controls fluid deliveryto the bladders 18 a-n. As is typically known for IPC systems, bladders18 a-n undergo alternate inflation and deflation cycles to provideintermittent compression. The control unit 26 also comprises a processor54 for monitoring VRT and determining patient compliance (describedbelow), though more than one processor may be employed without departingfrom the scope of the invention. Processor 54 in general is operable toexecute the various functions of the compression control unit describedabove and hereafter. For example, processor 54 executes softwareinstructions for monitoring sensor 22 and determining VRT and forincrementing the active therapy time accordingly. Moreover, processor 54is further configured for controlling operation of pump 42 and port 50during operation. The pressure transducer or sensor 22 is coupled viaconnection tubing to one of the bladders, bladder 18 b in theillustrated embodiment, for monitoring pressure in the bladder 18 b.Sensor 22 is preferably coupled to port 50, and in turn coupled tobladder 18 b via the same connection tubing as used by pump 42.Alternative connection means are possible as well. The monitoredpressure may be employed to determine venous refill time, or VRT, of thelimb during a VRT mode of the control unit 26. Referring to FIGS. 3A-3E,processor 54 is configured to execute computer-executable instructionsfor pressurizing the bladder 18 b, for example, to determine acustomized venous refill time for the bladder. In an embodiment, when itis desired to determine the venous refill time for the patient, controlunit 26 permits bladder 18 b to reach a compression pressure and thencauses it to depressurize until the pressure in that particular bladderreaches a lower value. The computer-executable instructions fordetermining the venous refill time comprise pressurizing the bladder 18b to a first compression pressure (e.g., 20 mm Hg) to move the blood inthe leg from a region (e.g., calf) underlying the bladder. Afterpressurizing the bladder 18 b to the first compression pressure, thepressure in the bladder is reduced to a refill pressure (e.g., 10 mm Hg)to allow the blood to reenter the region of the limb underlying thebladder (after approximately 2.5 seconds of depressurization).

The pressure in the bladder 18 b is then sensed by the pressuretransducer 22 until it is determined that blood flow has been completelyrestored to the region of the limb underlying the bladder. The timeelapsed to restore blood flow is characterized as a first venous refilltime t₁ and is stored by the controller 26. The bladder 18 b is thenpressurized to a second compression pressure (e.g., 30 mm Hg) and thesame process is performed as was performed for the first compressionpressure, resulting in a second venous refill time t₂. The bladder 18 bcan then be pressurized to even more compression pressures (e.g., 45, 60and 75 mm Hg) and the process performed for the first and secondcompression pressures can be repeated for each pressure level to producevenous refill times t₃, t₄, t₅, t_(n) for each additional pressurelevel. It is understood that pressure amounts other than those describedabove and shown in FIGS. 3A-3E can be used in the venous refill processwithout departing from the scope of the invention. Additionally, thevenous refill process at each pressure level can be performed multipletimes to produce multiple venous refill times for each pressure level.

Alternatively, the bladder under inspection could be permitted todepressurize for a predetermined period of time, or to depressurizefully and then be repressurized until the pressure reaches thepredetermined value, for example, 10 mm Hg. The pressure transducer 22senses the pressure in bladder 18 b for a time sufficient to allow thevenous system in the limb to refill, i.e., engorge with blood again. Thepressure as sensed by pressure transducer 22 rises as the limb expandsupon filling with blood and reaches a generally steady state when theleg has refilled. The time between the start of depressurizing thebladder 18 b and when this plateau occurs is measured to be the VRT.

For example, using the determined venous refill times t₁-t_(n), theprocessor 54 determines a customized compression pressure by plottingthe venous refill times for each selected pressure level on a graph asshown in FIG. 4 and fitting a best fit line to the plot using standardlinear regression analysis. The apex A of the best fit line correspondsto a customized compression pressure P_(c) for producing a maximumvenous refill time T_(max). The determined compression level P_(c) andrefill time Tmax are then incorporated into the compression therapy ofthe limb wherein the bladder 18 b in the garment, or sleeve, 14 isrepeatedly pressurized to the customized compression pressure P_(c),maintained at the customized compression pressure for a period of timeand subsequently reduced to the refill pressure for the determinedmaximum refill time T_(max) to facilitate blood circulation in the limb.

In the instance where multiple venous refill times are recorded for eachselected compression pressure level, the refill times are averaged bythe processor 54 to produce an average value for the given pressurelevel. These average values are then plotted and a best fit line is fitto the plot of the average values and the customized compressionpressure and maximum venous refill time are extrapolated from the plotin the same manner as described above. If the garment 14 includesmultiple bladders (e.g., ankle, calf and thigh bladders as shown inFIGS. 2A and 2B), the controller 26 can be configured to operate the IPCdevice 10 to apply sequential compression therapy to the limb using thecustomized pressure and maximum refill time.

In an additional or alternative embodiment, each time control unit 26determines VRT, it cycles (i.e., inflates and deflates) bladder 18 bthrough several values of compression pressure to obtain a correspondingVRT value for each value of compression pressure. The control unit 26then calculates a maximum VRT, or V_(max). V_(max) is ascertained bydetermining a best fit between the compression pressure values and thecorresponding VRT values via any suitable fitting method (e.g., linearregression analysis). Specifically, a maxima of the best fit designatedas V_(max). Desirably, instead of using individual VRT values, multipleVRTs are recorded and averaged for each compression pressure to providean average VRT value for each compression pressure value.

A custom compression pressure P_(c) is then determined corresponding toV_(max) and is designated as a target compression pressure of thecompression therapy regimen of bladder 18 b.

After applying compression therapy to the limb for a period of time theprocess for determining the customized compression pressure and maximumvenous refill time can be repeated to determine new values. Additionallyor alternatively, memory in the controller 26 can record the venousrefill times sensed by the pressure transducer 22 during the compressiontherapy and, for example, average the recorded values to adjust the timebetween consecutive pressurizations of the bladder 18 b based on theaveraged refill times. These two processes ensure that the compressiontherapy being delivered to the limb adapts to the changingcharacteristics of the limb so that a customized compression therapy isdelivered to the limb through the duration of the compression therapy.

As described above, processor 54 of the control unit 26 is responsive tothe output signal of pressure sensor 22 for determining the VRT asdescribed above. The unit 26 is further operable to monitor thedetermined VRT over time. Any aspect of the measured VRT may bemonitored, including, but not limited to: individual VRT values, averageVRT within a specific time window, average VRT within a moving timewindow. variations in VRT over multiple VRT measurements and/orcompressive cycles, the steady state pressure achieved during the VRTmeasurement, any compression cycle parameter, and so on.

Most patients have a normal VRT between 40-50 seconds for legmeasurements, with inanimate leg forms generating VRT values as low as30 seconds. A VRT of approximately 30 seconds is also typically observedwhen the garment 14 is not in use by the patient. Hence, the monitoredVRT may be used for determining whether the patient is using the garment14. Accordingly, in a preferred embodiment, control unit 26 stores andincrements an active therapy time when the monitored VRT either fallswithin a normal range (e.g., 30-60 seconds), or simply exceeds apredetermined threshold (e.g., 30 seconds), both of which are indicativeof normal usage of compression system 10. In this manner, the value ofactive therapy time is a measure of the patient wearing garment 14 andits sequential inflation and deflation. Alternatively, active therapytime is the cumulative time of controller operation during which thepatient is deemed compliant.

In another embodiment, control unit 26 comprises an alarm 58 indicatingto a user when the monitored VRT falls below the predeterminedthreshold. At this point, processor 54 ceases incrementing the activetherapy time until further action is taken. The alarm 58 may be one ormore of an audio alarm and a visual alarm. The user, typically thepatient or a clinician monitoring the patient, may respond to the alarm58 by indicating that the patient is indeed compliant, such as the casewhere a patient changes positions and causes an intermittent dip inmonitored VRT. In other words, the user overrides the alarm. The therapytime would then continue to be incremented.

When the clinician indicates continued compliance by overriding thealarm 58 triggered by a lower VRT value (than the predeterminedthreshold), control unit 26 resets or revises the predeterminedthreshold value to the lower VRT value measured at the time of theoverride. In this manner, alarm 58 will not be triggered again until themonitored VRT dips to the revised threshold value. This prevents alarm58 from becoming bothersome in the event the patient has or oftenachieves a lower VRT value for a justifiable reason such as uniquephysiology, posture, etc.

Alternatively, in response to alarm 58, the clinician may determine thatthe patient is not wearing the garment 14 and is therefore not beingcompliant with the compression regimen. The clinician may respond byturning off control unit 26, at which point the therapy time ceases toincrement. The therapy time may advantageously be stored in a memory 62,external or internal to processor 54, for continued measurement the nexttime the control unit 26 is started.

In yet another embodiment, control unit 26 has a configurable optionthat allows therapy time to continue to increment despite the monitoredVRT falling below the predetermined threshold. In this embodiment,accumulation of therapy time is halted only when a clinician turns offthe control unit 26, in response to alarm 58 or otherwise. Continuing toincrement the therapy timer in this manner permits the clinician toclosely track an operation time of control unit 26, referred tohereafter simply as controller operation time. This embodiment isbeneficial when monitoring patients with uncharacteristically low VRT,such as those suffering from venous insufficiency, for example. In sucha patient, low VRT measurements may erroneously indicate non-complianceduring use. The clinician with knowledge of the patient's condition canthen manually control accumulation of therapy time.

Determining patient compliance from active therapy time may be carriedout in a number of ways. In one embodiment, patient compliance is simplythe therapy time value. In another embodiment, patient compliance isspecified as a ratio between active therapy time and controlleroperation time.

In another embodiment, a shift time is monitored and has a specifiedvalue, such as 24 hours. Compliance is specified as a ratio betweenactive therapy time and shift time. Once monitoring is initiated, bothactive therapy time and shift time are continually evaluated. When theoperation time of the controller reaches the shift time (i.e., operationtime=24 hours), the compliance measurement is limited to a rolling24-hour (shift time) window. At any time point thereafter, activetherapy time and hence compliance is accounted for only over the last 24hours of operation. Desirably, shift time is programmable and resettableby a user. In this manner, a clinician or other healthcare provider canspecify his or her own shift time, and then observe how long the patienthas been compliant during the shift.

The control unit 26 further includes a controller interface 66. Adisplay 70 of the interface 66, as illustrated in FIG. 5A, displayspatient compliance as a percentage 74, wherein the percentage isevaluated as a ratio between the displayed active therapy time 76 andthe displayed shift time 78. The interface 66 includes a RESET option 82for resetting the timers. The display 70 also illustrates a VRTindicator 102 and a VRT value 106.

A user may further access a Compliance Graph 90 (see FIG. 5B) via agraph option 86 of the interface 66. Specifically, FIG. 5B illustrates arolling 24-hour window for monitoring compliance and shows a percentagecompliance 94. The exemplary user interface of FIG. 5B displays thepercentage compliance 94 along with a boxed representation of thetherapy time and shift time (denoted together by the reference character98) at various time points. The timers are reset at time point 100, andmonitored thereafter. In this example, compliance is approximately 90%for the first 24 hours (6 am-6 am), 100% for the 6 pm-6 pm slot, and 90%for the 12 midnight-12 midnight slot. Other means of displayingcompliance and the various timers are within the scope of the invention.

According to aspects of the invention, a method of monitoring patientcompliance is generally illustrated in FIG. 6 in the form of anexemplary flow diagram. Compliance monitoring is initiated or reset at402. At 404, a signal is continuously received from the pressure sensor22 coupled to the bladder 18 b. The signal is a function of bladderpressure, and is further indicative of a change of girth of the limb orbody part of the patient. The venous refill time or VRT of the limb isdetermined and monitored as a function of the received signal at 408. At410, a determination is made whether the monitored VRT exceeds thepredetermined threshold. If this is the case, the active therapy time isincremented at 414. The active therapy time and compliance is displayedto the user at 418.

If, at 410, the monitored VRT does not exceed the threshold, the alarm58 is initiated at 420. At 424, the user responds by either overridingthe alarm 58 or stopping the control unit 26. If the user chooses tooverride the alarm, 58, the threshold is set to the monitored VRT valueat 428, and the active therapy time continues to increment as describedabove. If the user chooses at 424 to stop the control unit 26, theactive therapy time is stored to memory 62 at 430, and the control unit26 shuts down at 432.

According to further aspects of the invention, a method of monitoringpatient compliance is generally illustrated in FIG. 7 in the form of anexemplary flow diagram. Compliance monitoring is initiated or reset at502. At 504, a signal is continuously received from the pressure sensor22 coupled to the bladder 18 b. The signal is a function of bladderpressure, and is further indicative of a change of girth of the limb orbody part of the patient. The venous refill time or VRT of the limb isdetermined and monitored as a function of the received signal at 508. At510, a determination is made whether the monitored VRT exceeds thepredetermined threshold. If this is the case, the active therapy time isincremented at 514. The active therapy time is correlated to compliance,and may further be displayed to the user, at 518.

If, at 510, the monitored VRT does not exceed the threshold, the alarm58 is initiated at 520. At 524, the user responds by either overridingthe alarm 58 or stopping the control unit 26. If the user chooses tooverride the alarm, 58, the threshold is set to the monitored VRT valueat 528, and the active therapy time continues to increment as describedabove. If the user chooses at 524 to stop the control unit 26, theactive therapy time is stored to memory 62 at 530, and the control unit26 shuts down at 532.

Having described aspects of the invention in detail, it will be apparentthat modifications and variations are possible without departing fromthe scope of the invention defined in the appended claims. For example,an upper predetermined threshold (e.g., 60 seconds) of monitored VRT maybe defined that triggers the alarm as well. In other words, the alarmmay be triggered above and below a predetermined range of normal VRTvalues, typically 30-60 seconds. The upper predetermined threshold maybe resettable as well. Additionally, more than one inflation bladder maybe connected to a different pressure sensor each, and the pressurereadings from several pressure sensors may then be combined in any waypossible to determine VRT and/or compliance.

The compliance percentage may, in addition to being indicatednumerically as illustrated, also be displayed via graphical elementssuch as a pie chart (not shown). Interface 66 is desirably an integrateddisplay with associated soft keys as illustrated, allowing the user toselect and browse various elements described above using the soft keys.However, other constructions of the interface 66 are within the scope ofthe invention.

To improve patient compliance with compression therapy, there is a needfor increasing clinician participation while providing the clinician autility for compliance notification and monitoring. Several requirementsmust be fulfilled to achieve this goal. The clinician should be notifiedwhen compliance is purportedly not being achieved. Further, theclinician should be able to decide whether to deem the patient compliantor not, and adjust compliance parameters to each patient. Finally, theclinician should be able to monitor the duration of compliance forspecific time periods, since they are more likely to be concerned withpatient compliance during their work shift(s). A user-friendlycompliance monitoring interface is provided for this purpose.

In view of the above, it will be seen that the several objects of theinvention are achieved and other advantageous results attained. FIGS. 8Aand 8B illustrate, during operation, a pressure cycle of inflatablebladder 18 b. Even when not in use by a patient, bladder 18 b reachespressure values (see FIG. 8A) that are similar to when the bladder 18 bis in use by a patient (see FIG. 8B). The difference in the curve peaksis merely 2-3 mmHg for the illustrated case. When monitored by apressure sensor, the pressure values correspond to internal bladderpressure, and cannot adequately account for actual usage of the garment14. Pressure profiles for measuring VRT, on the other hand, aredetermined by reducing bladder pressure to a refill pressure and closinga vent valve (as described above), followed by monitoring pressureincrease as blood re-enters the limb. Blood flow to the limb results inexpansion of the limb, which forces air out of bladder 18 b, backthrough connecting tubing and onto the sensor 22, which records anincrease in pressure. Processor 54 then evaluates the increase inpressure to calculate VRT and determines compliance.

FIGS. 9A and 9B illustrate the pressure profile as a refill curve ofbladder 18 b during VRT measurement. The illustrated pressure profilecompares two scenarios, namely, a) when garment 14 is not in use by apatient (see FIG. 9A) and b) during use by a patient (see FIG. 9B). Whenno blood flow is detected such as during non-use, an insignificantincrease in pressure is observed, a little less than 2 mmHg for theillustrated case and attributable to pressure stabilization. During use,on the other hand, a pressure change as high as 10 mmHg is observable(approximately 5.5 mmHg for FIG. 9B) in bladder 18 b due to distensionof the limb. Embodiments of the invention translate this detectablechange in pressure to VRT and for indication of compliance, therebyproviding a strong correlation between actual use and estimatedcompliance.

Additionally, by using the same pressure sensor and output to monitorVRT and usage, a controller is able to determine compliance withoutrequiring additional, cumbersome hardware on the garment itself

When introducing elements of the present invention or the preferredembodiments(s) thereof, the articles “a”, “an”, “the” and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

As various changes could be made in the above constructions, productsand methods without departing from the scope of the invention, it isintended that all matter contained in the above description and shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

1. A method of monitoring patient compliance with a compression therapyregimen, said method comprising: receiving a signal from a pressuresensor coupled to a compression garment, wherein the garment is sizedand shaped to be wrapped around substantially a limb of a wearer andcomprises one or more selectively inflatable bladders for applyingcompression to the limb upon inflation, said signal being indicative ofa change of girth of the limb; determining a venous refill time of thelimb as a function of the received signal; monitoring the determinedvenous refill time; and incrementing a patient compliance timer inresponse to the monitored venous refill time exceeding a predeterminedthreshold.
 2. The method of claim 1, further comprising indicating analarm condition when the monitored venous refill time falls below thepredetermined threshold.
 3. The method of claim 2, further comprisingoverriding the indicated alarm condition, by a user, to continue saidincrementing of the patient compliance timer.
 4. The method of claim 3,further comprising resetting the predetermined threshold to themonitored venous refill time when the indicated alarm condition wasoverridden.
 5. The method of claim 2, wherein the alarm condition is oneor more of an audio alarm and a visual alarm.
 6. The method of claim 1,further comprising providing a display representative of the patientcompliance timer to a user.
 7. The method of claim 1, further comprisingchanging a compression profile of the garment as a function of thedetermined venous refill time.
 8. A system for monitoring patientcompliance with a compression therapy regimen, said system comprising: acompression garment sized and shaped to be wrapped around substantiallya body part of a wearer, said garment comprising one or more selectivelyinflatable bladders for applying compression to the body part uponinflation; one or more fasteners for securing the garment in aself-retaining wrapped configuration around the body part; a pressuresensor coupled to at least one of the bladders, said sensor generating asignal indicative of a change of girth of the body part when the garmentis in the wrapped configuration; and a compression control unit, saidcontrol unit comprising: a pump for pressurizing fluid; an outlet portin fluid communication with the pump, said outlet port having fluidtubing connected thereto for selectively delivering pressurized fluid toat least one of the inflatable bladders; and one or more processorsreceiving and responsive to the signal generated by the pressure sensorfor: determining a venous refill time of the body part as a function ofthe received signal; monitoring the determined venous refill time; andincrementing a patient compliance timer in response to the monitoredvenous refill time exceeding a predetermined threshold.
 9. The system ofclaim 8, wherein the compression control unit comprises an alarmindicating when the monitored venous refill time falls below thepredetermined threshold.
 10. The system of claim 9, wherein thecompression control unit is responsive to user input for overriding thealarm to continue incrementing the patient compliance timer.
 11. Thesystem of claim 10, wherein the one or more processors is configured forresetting the predetermined threshold to a value corresponding to themonitored venous refill time when the alarm was overridden.
 12. Thesystem of claim 9, wherein the alarm is one or more of an audio alarmand a visual alarm.
 13. The system of claim 9, wherein the compressioncontrol unit comprises a display representative of the patientcompliance timer.
 14. The system of claim 9, wherein the one or moreprocessors increment the patient compliance timer when the monitoredvenous refill time is in a range of about 30-60 seconds.
 15. The systemof claim 14, wherein the predetermined threshold is approximately 30seconds.
 16. A method of monitoring patient compliance with acompression therapy regimen, said method comprising: receiving a signalfrom a pressure sensor coupled to a compression garment, wherein thegarment is sized and shaped to be wrapped around substantially a limb ofa wearer and comprises one or more selectively inflatable bladders forapplying compression to the limb upon inflation, said signal beingindicative of a change of girth of the limb when the compression garmentis wrapped substantially around the limb of the wearer; determining avenous refill time of the limb as a function of the received signal;monitoring the determined venous refill time; comparing the monitoredvenous refill time to a predetermined range of normal venous refilltimes; and correlating the monitored venous refill time to patientcompliance as a function of said comparing.
 17. The method of claim 16,said comparing further comprising indicating an alarm condition when themonitored venous refill time falls outside the range of normal venousrefill times.
 18. The method of claim 17, further comprising permittingmanual overriding of the indicated alarm condition and resetting therange of normal venous refill times based on the determined venousrefill time upon said manual overriding.
 19. The method of claim 16,further comprising providing a display representative of said correlatedpatient compliance.
 20. The method of claim 17, wherein the alarmcondition is one or more of an audio alarm and a visual alarm.
 21. Themethod of claim 16, wherein the range of normal venous refill times isabout 30 seconds to about 60 seconds.